Acoustics II: Kurt Heutschi recording technique. stereo recording. microphone positioning. surround sound recordings.

Transcription

1 demo Acoustics II: recording Kurt Heutschi

2 demo

3 Stereo recording: Patent Blumlein, 1931 demo in a real listening experience in a room, different contributions are perceived with directional information allows for a separation of direct sound and reflections thus a suitable recording method has to provide directional information two channels are needed to offer different signals to the two ears

4 Stereo recording: principle demo evaluation of directional information by the ear: level differences between the ear drums left and right time of arrival differences between the ear drums left and right

5 Stereo recording: principle directional information due to level differences at the ear drums demo

6 Stereo recording: principle directional information due to time of arrival differences at the ear drums demo

7 Stereo recording: principle demo direct stereo signal recording: two appropriately mounted s: indirect stereo signal recording: signals of several distributed directional s summed up to left and right stereo channels

8 demo

9 demo XY arrangement

10 XY arrangement demo two cardioid capsules orientation: 65 each, relative to frontal direction (opening angle: 130 ) capsules close to each other

11 XY arrangement demo correct wrong

12 XY arrangement demo advantage: good suppression of sources on the rear side disadvantage: frontal direction does not correspond to axis non ideal off-axis frequency response

13 demo MS arrangement

14 demo MS arrangement one omni (or a cardioid) and one figure of eight omni Mid figure of eight Side capsules close to each other

15 MS arrangement demo stereo signal is formed as: left = M + β S right = M - β S β adjusts the opening angle

16 MS arrangement demo advantages: opening angle can be adjusted electronically with high quality storing media, recording of M and S for later formation of left and right (opening angle remains adjustable) disadvantage: high sensitivity for rear sided sources

17 demo Blumlein arrangement

18 Blumlein arrangement demo two figure of eight s 90 different orientation capsules close to each other

19 Blumlein arrangement demo advantages: - disadvantages: high sensitivity for rear sided sources low frequency weakness of figure of eight s

20 demo

21 demo AB arrangement

22 AB arrangement two omnis laterally separated by typically 20 cm demo

23 AB arrangement demo increased lateral separation for larger distances to the source often used for recording of classical music in churches and concert halls advantage: omnidirectional s with excellent properties available disadvantage: high sensitivity for rear sided sources

24 demo

25 demo ORTF arrangement

26 ORTF arrangement demo two cardioid s orientation: 55 each, relative to frontal direction (opening angle: 110 ) laterally separated by 17 cm

27 ORTF arrangement demo advantage: phantom sources distributed homogeneously on stereo basis disadvantage: frontal direction does not correspond to axis non ideal off-axis frequency response

28 demo Jecklin disc

29 Jecklin disc demo two omnis laterally separated by 17 cm separating disc of 30 cm in diameter in between

30 Jecklin disc demo

31 Jecklin disc demo advantage: omnidirectional s with excellent properties available disadvantages: problem of comb filter in case of insufficient absorption of the disc high sensitivity for rear sided sources

32 demo Binaural stereophony

33 demo Binaural stereophony two omnis mounted at position of ear drums in an artificial head

34 Binaural stereophony demo correct frequency response distortions due to outer ear and ear canal (head related transfer function) suitable for play- by headphones, optimal if headphone is compensated for transfer function headphone-membrane ear drum excellent reproduction of spacial impression however, front- localization not always perfect (visual information is missing) caution: unsuitable for reproduction by loudspeakers (head related transfer function occurs two times)

35 demo Binaural stereophony: localization test (JAES, vol. 47, p.83, 1999) experiment: listener sitting in a highly damped room, RT about 0.3 sec 19 visible loudspeakers arranged around listener listener has to identify active speaker localization accuracy procedure: phase 1: reproduction by real speakers phase 2: binaural recording with artificial head and reproduction by headphones

36 Binaural stereophony: localization test results for loudspeaker reproduction: demo

37 Binaural stereophony: Ortungstest results for binaural recording and headphone reproduction: demo

38 demo demo: spacial mapping of various recording arrangements

39 demo: spacial mapping (CD: Stereo Microphone Technique) demo clicks radiated by one speaker after the other

40 Demo: spacial mapping demo various stereo arrangements: A B C D

41 Demo: spacial mapping demo various stereo arrangements: A B C D XY AB MS ORTF

42 demo

43 demo a recording aims at capturing: the source signal information about the room strategies: stereo pair stereo pair + room distributed s

44 Stereo pair demo find optimal distance to source! if distance is too small: recording too dry extended source (orchestra) if mapped inhomogeneously if distance is too large: recording too reverberant and too blurry optimal distance for strength direct sound strength diffuse sound critical distance caution: sources or s with pronounced directivity enlarge the critical distance

45 Stereo pair + room demo stereo pair relatively close to the source room (omni) in the diffuse field balance between direct and diffuse sound adjustable during mixing

46 Distributed s demo separate s for each instrument or group of instruments left-right mapping with help of panorama control distance mapping by adding artificial reverberation difficulties: interferences between the signals of different s (large level differences between mics necessary) early reflections at surfaces comb-filter effects (solution: pressure zone s)

47 demo demo

48 demo demo (CD: United Music of Marantz I) different arrangements: A B C

49 demo demo (CD: United Music of Marantz I) different arrangements: A B C XY Jecklin distributed s

50 demo

51 demo capabilities of Stereo: generation of phantom sources within a listening angle of 60 good direct sound reproduction of the sources on stage capabilities of Surround: listening angle: 360 good direct sound reproduction of the sources on stage reproduction of rear lateral reflections accurate room information

52 : format demo most common format: 5.1 (developed for movie theatres) 6 discrete channels: Front Left Front Right Front Middle Rear (Surround) Left Rear (surround) Right LFE (low frequency effects: Hz

53 Surround sound : perspectives direct/ambient perspective of listener in the audience demo arrangement: front channels: stereo pair surround channels: more distant omnis or cardioids oriented to rear side

54 Surround sound : perspectives inside the band musicians perspective demo arrangement: front channels: distributed s surround channels: distributed s for each group of instruments

55 demo assessment of recording quality

56 assessment of demo Guideline: EBU (European Broadcasting Union), Tech. 3286, 1997 assessment categories: Spatial impression Stereo impression Transparency Sound balance Timbre Freedom from noise and distortions

57 assessment of demo Spatial Impression (reproduction of plausible environment): homogeneity of spatial sound reverberance acoustical balance apparent room size depth perspective sound color of reverberation sound example criterion reverberance: too dry too reverberant appropriate

58 assessment of demo stereo impression (reproduction of correct and plausible directions of the sources): directional balance stability sound image width location accuracy sound example sound image width: too narrow too wide appropriate

59 assessment of demo transparency (reproduction can be heard in all its details): sound source definition time definition intelligibility sound example: sound source definition: muddy clear

60 assessment of demo sound balance (all sources appear with comparable loudness): loudness balance dynamic range sound example: loudness balance: trombone too weak trombone too loud trombone appropriate

61 assessment of demo timbre (correct reproduction of the characteristics of the sources): sound colour sound attack sound example: sound attack: attacks are not precise precise attacks

62 assessment of demo freedom from noise and distortions (no audible noise components or distortions): sound example noise: noise by audience

63 demo eth-acoustics-2